Physics - Radioactivity

Atoms with the same number of protons but different numbers of neautrons. Therefore they have the same atomic number, but different mass numbers

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What does a radioactive substance contain?

Unstable nuclei that becomes stable by emitting radiation

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What happens when an unstable nuclei undergoes radioactive decay?

It emits radiation

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Where does background radiation come from?

Radioactive substances that are in the environment and man-made sources

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What are the three types of radiation?

Alpha, beta and gamma radiation

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What does an alpha particle consist of?

Two protons and two neutrons

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What is an alpha particles relative mass and charge?

Its relative mass is 4 and relative charge is +2

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What happens when a nucleus emits an alpha particle?

The nucleus loses 2 protons and 2 neutrons so the atomic number goes down by two and the mass number goes down by four

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What does beta radiation consist of?

Particles which are high speed electrons

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What is a beta particles relative mass and charge?

Its relative mass is 0 and its relative charge is -1

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What happens when a nucleus emits a beta particle?

The atomic number goes up by one and the mass number is unchanged

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What is a gamma ray?

An electromagnetic wave which has no charge and no mass

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What happens when a nucleus emits a gamma ray?

There is no change in the atomic number or the mass number

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What is the process of ionisation?

When nuclear radiation travels through a material and it collides with atoms of the material, knocking electrons off the atoms, creating ions

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What does ionisation in a living cell do?

Damage or kill the cell

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List the three types of radiation from most to least ionising

Alpha, beta, gamma

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Why are alpha particles more strongly ionising than beta particles?

Because they have twice as much charge and they move more slowly than beta particles so they collide with atoms more often than beta particles do

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Why are beta particles more strongly ionising than gamma rays?

Because they are charged whereas gamma rays are uncharged and they are slower than gamma rays

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What absorbs alpha radiation and what is its range in the air?

It is absorbed by thin paper or human skin and its range is about 5cm

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What absorbs beta radiation and what is its range in the air?

It is absorbed by 5mm of aluminium and its range is about 1m

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What absorbs gamma radiation and what is its range in the air?

It is absorbed by several cm of lead or several metres of concrete and its range is unlimited

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Where are alpha particles deflected by electric and magnetic fields and why?

Towards the negative plate because alpha radiation has a positive chrge

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Where are beta particles deflected by electric and magnetic fields and why?

Towards the positive plate because beta radiation has a negative charge

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Why are gamma rays not deflected by electric and magnetic fields?

Because they are uncharged

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What is the half-life of a radioactive isotope?

Either the average time it takes for the number of nuclei of the isotope in a sample to halve or the time it takes for the count rate from a sample containing the isotope to fall half its initial level

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What are alpha sources used in?

Smoke alarms

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How are alpha particles used in smoke alarms?

The alpha particles ionise the air molecules in a circuit gap so an ionisation current passes across the gap. Smoke absorbs the ions and reduces the current to 0 which switches the alarm on

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What are beta sources used for?

Thickness monitoring in the manufacture of the things like paper or metal foil

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How are beta particles used for thickness monitoring?

Rollers squeeze the material so a thin continuous sheet of material emerges. A radiation detector monitors the radiation passing through the material from the source on the other side of the sheet

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What are gamma and beta particles used as?

Tracers in medicine

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How are gamma and beta particles used as tracers?

The source is injected or swallowed by the patient. Its progress around the body is monitored by a detector outside the patient